I don't mean just a "no signal" situation, I mean XM no longer even appears on the screen. I'm just guessing, but if you're losing the xm stuff it could be either the head unit itself or the break out xm receiver (if the cars even have one -- like the traditional receivers after market head units use for satellite radio).

Shifting the band button scrolls through FM and AM but no XM. The only reason I bring up my electrical problems is because I bet the dealers have probably seen a fair ammount of electrical problems with these newer model vehicles that have all these extra features.